The present invention relates to a light-emitting device and, in particular, to a silicon-based laser device.
The addition of optical functional capabilities to electronic microcircuits integrated on silicon chips is an objective which is of the greatest importance in the telecommunications field and in the development of electronics, optoelectronics and photonics circuits and materials.
A coherent light source (a laser) is a key element in optoelectronic applications.
As is well known, silicon is the currently-preferred semiconductor and is widely used in electronic circuits, owing to its physical properties, its reliability, and its low cost.
Silicon is a semiconductor with an indirect band gap and the very poor properties of the material as a light-emitting source are due to this characteristic. In fact, in order for light emission to occur, a further energy-transfer process (interaction with phonons) has to take part in the recombination of the charge carriers, and non-radiative recombinations are more likely than radiative ones.
For this reason, silicon has always been considered unsuitable for optoelectronic applications and the integration of optical elements with microelectronic circuits is currently achieved with the use of compound semiconductors with direct band gaps, in particular, compounds of groups III-V.
Advanced composite semiconductor laser devices adopt, as the active medium for achieving optical amplification, single-dimensional quantum structures (quantum dots) or two-dimensional quantum structures (quantum wells).
It is known that the properties of silicon depend on its structure on a nanometric scale and it has recently been shown that it is possible to bring about light emission at ambient temperature when the silicon forms a single-dimensional or two-dimensional quantum structure.
Silicon-based electroluminescent devices have therefore been produced, for example, as described by K. D. Hirschman, L. Tsybeskov, S. P. Duttagupta and P. M. Fauchet in Nature 384, pages 338-340 (1996), in an article entitled xe2x80x9cSilicon based light emitting devices integrated into microelectronic circuitsxe2x80x9d.
Silicon nanostructures (for example, porous silicon) can emit light as a result of the quantum confinement of the carriers if they are stimulated by light of short wavelength of the order of 488 nm, as documented in the article entitled xe2x80x9cSilicon quantum wire array fabrication by electrochemical and chemical dissolution of wafersxe2x80x9d by L. T. Canham which appeared in the journal Appl. Phys. Lett. 57, pages 1045-1048 (1990).
In spite of the interesting properties of porous silicon, it is not very suitable for the production of commercial devices because of the large internal surface of its structure which is highly reactive and results in characteristics of the material which are greatly dependent on the atmosphere in which it is immersed. Moreover, in microelectronic applications, the manufacturing processes, which take place in a moist environment, are somewhat incompatible with the dry manufacturing processes which are typical of the manufacture of integrated semiconductor electronic circuits.
However, up to now, it has not been possible to achieve optical gain and stimulated emission and thus to produce devices which emit coherent light (lasers) since silicon shows efficient absorption of the free carriers, which reduces the net gain available for the laser effect.
The object of the present invention is therefore to provide a satisfactory solution to the problems set out above, by providing a silicon-based device for emitting coherent light, and a silicon-based material therefor.
According to the present invention, this object is achieved by means of a light-emitting device having the characteristics recited in claim 1.
Particular embodiments of the invention are defined in the dependent claims.
Another subject of the invention is a chip according to claim 18.
Still another subject of the invention is a material according to claim 20.
In summary, the present invention is based on the principle of achieving optical gain on the basis of an active region comprising a set of amorphous or crystalline silicon nanostructures, preferably with radii of the order of 1.5 nm, placed in a silicon dioxide substrate so as to form a high-density thin layer buried beneath the surface of the sample in question.
Further characteristics and advantages of the invention will be explained in greater detail in the following detailed description, given by way of non-limiting example with reference to the appended drawings.